I want to mix Navy Grogs, but one of the people that will be drinking them can't drink grapefruit juice due to her medication. What do you think would be the best substituion in the recipe for recreating the flavor? I'm going to be using Don the Beachcomber's recipe. Thanks!

Just grapefruit juice or any citrus juice? A Navy Grog contains just as much lime juice as grapefruit. If it's just grapefruit that's the problem, I would think pomelo would be the closest thing, followed by maybe a combo of orange and lemon juices.

If all citrus juice is out, you can sub any number of juices - guava, pineapple, etc., just know that none of them taste like grapefruit.
_________________"I am Lono!" -- Hunter S. Thompson

It's specifically grapefruit juice, not other citrus juices. Specifically, this is the case for people on certain kinds of cholesterol medication. lol I definitely want to go for a similar flavor profile.

Grapefruit juice can prevent the metabolism of many medications, meaning it can cause a low dose and then, when the grapefruit is out of the system, a high dose as everything in you suddenly gets broken down. Good on you for considering that! I forgot myself and was happily chugging grapefruit juice until I realized I wasn't feeling right. Whoops.
_________________"You can't eat real Polynesian food. It's the most horrible junk I've ever tasted." —Trader Vic Bergeron

A grapefruit is a hybrid of an orange and a pomelo so a pomelo would not work as a substitute.
Grapefruits have such a distinct flavor profile I'm not sure what a good substitute would be. Maybe tangerine and orange juice?

Hmmm... one of the common misconceptions is that the flavor of grapefruit is "sour" when in reality it is more bitter unless you are using the ruby red variety.

What you might think about doing is using grapefruit bitters (or the flavoring noted) and replacing the volume with a lighter mixer. You could, I cannot believe I am writing this, also try a grapefruit soda like fresca or San Pellegrino grapefruit. As the Furanocoumarin appears to be negligible, according to papers, in the soft drinks. Just also be sure to adjust the sugar levels if your mixers are sweeter than normal grapefruit juice.

You could also just serve them the Trader Vic's Grog since that uses no grapefruit.

Perhaps tart cherry juice diluted with something mildly sweet or mildly sour like passion fruit or lemon juice? Or just water it down a bit as it is far more bitter and less citric than grapefruit.
_________________Announcing Swank Pad and Crazy Al's Molokai Maiden!

Good topic --- I too, am not supposed to have grapefruit juice right now, though I'm wondering what the effect of small amounts, like the half ounce in a Jet Pilot, would be. Grapefruit bitters might be the way to go, cause there's nothing quite like that taste.

It kind of depends on what the drug is for and when you would be taking it in relation to the consumption of the juice. As the effect can last up to a day, so it would be like missing a days worth of doses. If it isn't a life critical medication, such as a seasonal allergy one, then you would be fine.

You could also look into some hybrids that lack furanocoumarin in them, and juice them for cocktails if they are for sale near you.